JPH06275372A - Induction heating cooking device - Google Patents

Abstract

PURPOSE:To provide an induction heating cooking device which has low common mode noise leaked into a commercial power supply. CONSTITUTION:A series circuit of a filter capacitor 2 and a resistor 22, the absolute value of which is reduced substantially in proportion to a frequency up to the vicinity of a predetermined frequency and becomes substantially constant at the frequency of not less than a predetermined frequency or a series circuit of a filter capacitor 23 and a resistor 24 is connected between the potential of an input alternating-current power supply and a grounded rack 32. Thereby, an induction heat cooking device which has low common mode noise leaked into a commercial power supply in the wide range of a frequency region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker.

[0002]

2. Description of the Related Art In recent years, induction heating cookers which induce eddy currents in the bottom of a load pan by a high-frequency magnetic field to heat them have been attracting attention as a clean, safe, and highly heat-efficient cooking means. , High output is achieved.

A conventional induction heating cooker will be described below with reference to FIG. As shown in the figure, a power cord 2 with one end connected to a power plug 1 for connecting to a commercial power source
Reference characters a and 2b are connected to input terminals B and B'inside the housing 3 which houses electric parts and is made of a conductive material. In order to prevent electric shock, the power plug 1 has a ground terminal and is connected to the ground coil 14 via a ground wire 2c, and the other end of the ground coil 14 is connected to the conductive portion of the housing 3. The capacitor 5 and the input terminal of the common mode choke coil 6 are connected between the input terminals B and B ′, and between the output terminal of the common mode choke coil 6, the capacitor 8 and the input terminal of the full-wave rectifier 9 and the capacitor 7 a and the capacitor 7 a. 7b series circuits are connected to each other. Also capacitor 7
The connection point of the series circuit of a and the capacitor 7b is connected to the housing 3. A capacitor 10 is connected between the output terminals of the full-wave rectifier 9, and a choke coil 11 is connected in series to the positive electrode. The load side terminal of the choke coil 11 is connected to the input terminal A of the inverter 4 which is a kind of frequency conversion device, and the negative output terminal of the full-wave rectifier 9 is the inverter 4.
Is connected to the input terminal A '. The inverter 4 includes a heating coil 12 and a high frequency circuit section 13 that supplies a high frequency current to the heating coil 12.

The operation of the induction heating cooker configured as above will be described below. The high frequency circuit unit 13 includes a resonance capacitor that resonates with the heating coil 12, a high frequency power supply capacitor that bypasses a resonance current, and a semiconductor switching element. The resonance circuit of the heating coil 12 and the resonance capacitor is excited by switching of the semiconductor switching element. As a result, a high frequency large current is generated in the heating coil 12. The heating coil 12 as well as the high frequency circuit section 13 generate a high frequency radiated electromagnetic field in the surroundings. In the high-frequency circuit section 13, there is a semiconductor switching element or the like, and a breaking current having a steeper current change rate is generated in addition to the current supplied to the heating coil 12, so that a radiated electromagnetic field including a higher frequency component is generated.

The high-frequency voltage which could not be filtered by the high-frequency power supply capacitor inside the high-frequency circuit 13 is high-frequency circuit 1.
It is superimposed on the low frequency pulsating current DC voltage between the input terminals A and A'of No. 3. This superposed high frequency noise is so-called normal mode noise, and the choke coil 11 and the capacitor 1
0, the capacitor 8 and the capacitor 5 suppress the leakage from the input terminals B and B ′ to the commercial power source side.

Further, since the electric parts and their connecting lines forming the inverter 4 are close to the housing 3 and the power supply line through which the low-frequency current flows, the above-mentioned high-frequency radiated electromagnetic field also flows through the power supply through which the low-frequency current flows. High frequency noise is induced between the lines or between the power supply line and the housing 3. In the high frequency noise induced between the power lines of the low frequency part and the high frequency noise induced between the power line of the low frequency part and the housing 3, those having different phases in each power line become normal mode noise. Filtered.

In the high-frequency noise voltage induced by the high-frequency radiated electromagnetic field between the power line in the low-frequency section inside and the housing 3, what is in phase with each power line is so-called common mode noise. , Choke coil 11, common mode choke coil 6, capacitor 7a, capacitor 7
b, the leakage conduction noise to the commercial power source side which is filtered by the earth coil 14 is suppressed to a low level.

[0008]

However, the above configuration has a problem that even if the capacitors 7a and 7b are connected, the common mode noise level is not reduced in a range higher than a specific frequency, or conversely increases. Further, when the earth coil 14 is connected, there is a problem that the inductance component resonates with the capacitances of the capacitors 7a and 7b, and common mode noise increases in the vicinity of a specific frequency. Further, the earth coil 14 normally has a heavy weight such as ferrite. The core of the material is required and becomes heavy, and it is necessary to increase the diameter of the winding in order to prevent disconnection and abnormal heat generation even if a large current flows in the winding at the time of leakage, and the overall shape of the coil becomes large. However, it is necessary to secure a large space inside the device when mounting it on the device, and it takes time to mount it. There was a problem.

The present invention is to solve the above problems. In an induction heating cooker having a structure in which the conductive portion of the main body casing or internal parts is grounded to prevent electric shock, a common range over a wide range from low frequencies to high frequencies is provided. The purpose is to suppress modal noise components with small components that are easy to mount on equipment.

[0010]

In order to achieve the above object, the present invention provides a frequency conversion device for inputting electric power from a DC power supply or a low frequency power supply to generate a high frequency current in a heating coil for inductively heating a load. And a housing that houses some or all of the components that make up the frequency conversion device,
A grounding means for grounding a conductive portion of the housing or a component attached to or arranged in the housing to a ground;
Between the DC power supply potential part or the low frequency power supply potential part input to the frequency conversion device and the conductive part of the casing grounded to the ground by the grounding means, or the DC power supply potential part or the low frequency power supply potential part. Has a series resistance component of several tens ohms or more and approximately 10 kilohms or less between a conductive part of a component that is grounded to the ground by the grounding means and is attached to or disposed in the housing, up to a predetermined frequency. Is a configuration in which an impedance whose absolute value decreases substantially in proportion to the frequency is connected.

[0011]

With the above structure, the DC power supply potential portion or the low frequency power supply potential portion input to the frequency conversion device and the conductive portion of the casing grounded to the ground by the grounding means, or the DC power supply potential portion or the low power supply potential portion. Since the impedance is connected between the frequency power supply potential part and the conductive part of the component which is grounded to the earth by the grounding means and is attached or arranged in the case, the case in which the input power supply potential part is grounded High-frequency common-mode noise generated between the conductive parts of the above or between the conductive parts of the parts that are grounded and connected to the input power supply potential part or that are attached to or disposed in the housing are bypassed by the above impedance. The common mode noise can be suppressed from leaking to the power supply side outside the housing.

On the other hand, high-frequency noise of about 500 [kHz] or more, which is bypassed from the input power source potential portion on which the common mode noise is superimposed, through the impedance, to the conductive portion of the case or the conductive portion of the component which is grounded. When the amount of the component increases, this high frequency noise component is radiated from the conductive part of the housing or parts to the surrounding space, and the power supply line outside the housing for supplying DC power or low frequency power supplies this radiated noise. When the noise is received, the noise reaches the DC power supply or low frequency power supply which is the external power supply, and returns from the grounding part of the power supply to the grounding means of the induction heating cooker to the conductive part of the housing or the conductive part of the component. In this way, the high-frequency noise component generated in the frequency converter of the induction heating cooker leaks to the external power supply, and damages other electronic devices connected to the same power supply. There is a Les.

However, as described above, the absolute value of the bypass impedance decreases substantially in proportion to the frequency, that is, the higher the frequency, the smaller the absolute value.
Since the magnitude of the absolute value of impedance does not depend on the frequency, it has a series resistance component of about 10 ohms or more and about 10 k ohms or less, so the absolute value is equal to the resistance value at frequencies above the specified frequency. When the bypass impedance includes a small inductance component, it becomes larger, and the component of common mode noise in the vicinity of a predetermined frequency or higher is a conductive part or part of the grounded casing via the impedance. Is suppressed from being excessively bypassed to the conductive part of the housing, and is radiated to the surroundings from the conductive part of the housing or the conductive part of the component attached to or arranged in the housing to the external DC power supply or low frequency power supply side. The leaked high frequency noise can be suppressed.

On the other hand, at low frequencies below a predetermined frequency, the bypass impedance has a capacitive characteristic that the impedance decreases in proportion to the frequency, so that it is sufficient for external low frequency power frequencies such as commercial power sources. It is possible to have a large absolute impedance,
The external low-frequency power supply frequency component current flows into the bypass impedance or the chassis, and the direct current resistance component of the bypass impedance heats up and suppresses the increase in the current flowing through the ground wire when there is no abnormality. Increases the amount of common mode noise that bypasses the conductive parts of the case or parts that are grounded via the power supply, and attenuates the common mode noise that leaks to the external power supply in proportion to the frequency up to the specified frequency. It can be reduced by increasing the amount.

Further, since the impedance has a substantially constant resistance characteristic in a high frequency band above a predetermined frequency, a small inductance in a leakage path of common mode noise from the frequency converter to the external power source. The resonance characteristics of the component and the capacitive impedance component can be relaxed, and an increase in leakage noise near a specific resonance frequency can be suppressed.

[0016]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a commercial power supply 15 of 200 [V] having a frequency of 50 [Hz] or 60 [Hz] is
The power supply line 16a and the power supply line 16b are connected. A ground wire 16c is connected to the ground. To the terminals of the power plug 17, the power cords 18a and 18b and the ground wire 18c, which are integrally molded with resin, are connected,
The other terminal of the ground wire 18c is connected to the conductive portion of the casing 32 by the casing 3
2 The power cords 18a, 18 are provided to the input terminals C, C'inside.
The other terminals of b are connected to each other. 0.56 capacity
The filter capacitor 19 of [μF] has input terminals C and C ′.
The input terminal of the common mode choke coil 20 is connected to the input side of the common mode choke coil 20. 0.56 [μ is placed between the output terminals of this common mode choke coil 20.
F] filter capacitor 25 and full-wave rectifier 26
The AC input terminal of is connected.

A series circuit of a filter capacitor 21 and a resistor 22 and a series circuit of a filter capacitor 23 and a resistor 24 are respectively provided between both output terminals of the common mode choke coil 20 and the conductive portion of the housing 32 connected to the ground. It is connected. The capacitances of the filter capacitors 21 and 23 are both 2200 [pF], and the resistors 22 and 24 both have a resistance value of 200 [ohm].

A choke coil 28 of about 300 [μH] is connected to the positive terminal of the output of the full-wave rectifier 26, and a 2.2 [μF] capacitor 27 is connected between the output terminals of the full-wave rectifier 26. ing. An inverter 30 is provided between the load side terminal of the choke coil 28 and the negative terminal of the full-wave rectifier 26.
Input terminals D and D'of are connected. Inverter 30
Is composed of a heating coil 29 and a high-frequency circuit section 31, and the high-frequency circuit section 31 is a resonance capacitor 31c forming a resonance circuit with the heating coil 29, reverse conducting transistors 31a and 31b for exciting the resonance circuit by switching, a switching current or a resonance current. A high frequency power supply capacitor 31d that bypasses the control circuit, a control circuit 31e that controls on / off of the transistors 31a and 31b, and the like are included.

The operation of the induction heating cooker configured as described above will be described. When the induction heating cooker is operated, the transistor 31a of the high frequency circuit section 31,
31b is alternately turned on and off repeatedly, and the heating coil 2
9 and the resonance capacitor 31c resonate, so that the heating coil 2
A high-frequency current of about 20 [kHz] is generated at 9. The high frequency current generated in the heating coil 29 has a large current value but a substantially continuous waveform, and no sharp current flows. On the other hand, the transistors 31a and 31b of the high frequency circuit unit 31 and the high frequency power supply capacitor 31d include the transistors 31a and 31b.
A large current having a sharp current change according to the on / off of the current flows.

As described above, a large current or a high voltage including a wide frequency spectrum is applied to the inverter 30, and these currents or voltages generate an electromagnetic field having a spectrum distributed over a wide frequency range. This electromagnetic field generates a noise current and a noise voltage on the connection line connecting the electric parts inside the housing 32. Among these noise currents and noise voltages, normal mode noise superimposed between commercial power supply lines to which current and voltage of commercial power supply frequency are applied or between output terminals of the rectifier 26 is choke coil 28, filter capacitor 27, filter capacitor 25, filter. It can be suppressed by the capacitor 19.

On the other hand, a voltage value is induced between the commercial power line or the output terminal of the rectifier 26, which is induced between the ground line or the case 32 connected to the ground and the electric parts of the inverter 31 or the connecting line connecting them. Common-mode noise that changes in the same phase with respect to the ground is caused by the common-mode choke coil 20 and the filter capacitor 21 connected between the load-side terminal of the common-mode choke coil 20 and the grounded conductive portion of the housing 32. This can be suppressed by the series circuit of the resistor 22 and the series circuit of the filter capacitor 23 and the resistor 24.

For comparison, if the resistors 22 and 24 in FIG. 1 are not used, that is, if they are short-circuited and connected while leaving the filter capacitors 21 and 23, according to the experiment, the filter capacitors 21 and 23 are not used ( About 100 [kHz] to about 500 compared to the case of (open)
In the frequency band of [kHz], the effect of suppressing the amount of leakage of common mode noise to the commercial power source increases in proportion to the frequency, but in the frequency band of about 500 [kHz] or higher,
On the contrary, as the frequency becomes higher, the effect of suppressing the amount of leakage tends to decrease, and further, in the frequency band with a specific width of high frequency, the effect of suppressing locally decreases further, and the high frequency noise leaking to the commercial power source becomes extremely large. It could be high.

On the other hand, as in the embodiment of FIG. 1, the resistor 22 and the resistor 24 are connected to the filter capacitor 21 and the filter capacitor 2 respectively.
3 are connected in series to each other, the common mode of the capacitors 21 and 23 in the frequency range of 100 [kHz] to about 500 [kHz] is compared to connecting the filter capacitors 21 and 23 individually. Noise filtering effect is slightly reduced, but about 500 [kHz]
A great reduction effect was obtained at the above frequencies.

The action of the series impedance of the filter capacitor 21 and the resistor 22 and the series impedance of the filter capacitor 23 and the resistor 24 will be described below. About 5
When the frequency becomes higher than 00 [kHz], the radiation energy to the space becomes large, so the radiation efficiency of the electromagnetic wave of the antenna fed from the noise source becomes high, and the receiving efficiency of the antenna receiving the electromagnetic wave propagating in the space is also good. Become. Therefore, if such a high-frequency noise is supplied to a large area such as the conductive casing 32, it becomes a transmitting antenna and is easily radiated to the surroundings.
If there is a long conductor such as 8a and the power supply line 18b, it serves as a receiving antenna, and is susceptible to the induction of noise radiated into the space from the housing 32 or the like.

The absolute value │Z│ of the combined impedance of the series circuit of the capacitor and the resistor is represented by (Equation 1) where C is the capacitance of the capacitor, R is the pure resistance value of the resistor, and f is the frequency.

[0027]

[Equation 1]

The frequency characteristic of | Z | in the above equation is shown in FIG. A broken line a in FIG. 2 shows the frequency characteristic of the absolute value of the impedance of the resistor alone, and a broken line b in FIG. 2 shows the frequency characteristic of the absolute value of the impedance of the capacitor alone. As shown in FIG. 2, the combined impedance | Z |
At frequencies below 0 = 1 / (2 * π * R * C), the capacitor capacitance C is almost dominant and decreases in proportion to the frequency. At frequencies above the frequency f0, the resistance value R is almost constant. Become. In this embodiment, R = 200 [ohm],
Since C = 2200 [pF], f0 = about 362 [kH
z], the absolute value of the impedance of the series circuit of the filter capacitor 21 and the resistor 22 or the series circuit of the filter capacitor 23 and the resistor 24 is about 400
Below [kHz], it is almost equivalent to the case where a 2200 [pF] capacitor is connected alone, and is about 400 [kHz].
At the above frequencies, it is almost equivalent to a resistance of 200 [ohm] alone connected.

In the above embodiment, the series circuit of the filter capacitor 21 and the resistor 22, and the filter capacitor 23
Since the series circuit of the resistor 24 and the resistor 24 is connected between the commercial power supply potential on the load side of the common mode choke coil 20 and the housing 32, the common mode noise in the frequency range of about 400 [kHz] or less is generated by the common mode choke. The filter capacitor 21 is blocked by the inductance of the coil 20.
The case 32 is composed of a series circuit of the filter capacitor 21 and the resistor 22 which is substantially equivalent to the magnitude of the impedance of a single element, and a series circuit of the filter capacitor 23 and the resistor 24 which is substantially equivalent to the magnitude of the impedance of the individual filter capacitor 23.
The common mode noise that is bypassed to the commercial power source and leaks to the commercial power source side can be filtered by increasing the suppression amount in proportion to the frequency.

Further, the frequency component of 400 [kHz] or more of the common mode noise of the commercial power supply potential is blocked by the inductance of the common mode choke coil 20, and the impedance of the resistor 22 is substantially equal to the filter capacitor 21 and the resistor 22. Of the filter capacitor 23 and the resistor 24, which are approximately equal to the impedance of the resistor 24, are bypassed to the casing 32, but the impedance of the capacitor alone becomes smaller in proportion to the frequency. Unlike bypassing, bypassing is performed with an impedance of a substantially constant magnitude that does not depend on frequency, so that excessive supply of high-frequency components of common mode noise to the housing 32 is suppressed.

By suppressing excessive supply of the common mode noise component of about 400 [kHz] or more to the housing 32, about 500 [kHz] of large radiant energy is obtained.
The common mode noise component Vn is radiated to the surrounding space by using the housing 32 as an antenna, and the nearby power supply lines 18a,
18b serves as a receiving antenna and can be prevented from jumping over the common mode choke coil 20 and leaking to the commercial power supply 15 along the path shown by the broken line in FIG. In addition,
The capacitor 33, the resistor 34, the capacitor 35, and the resistor 36 in FIG. 1 are for evaluating the amount of conduction noise leaked to the outside of the device, and it is common to measure the voltage Va and the voltage Vb to evaluate the magnitude. is there.

When filter capacitors 21 and 23 having a small capacitance value of 2200 [pF] are connected between the commercial power source potential and the case 32 grounded, the leakage of the common mode noise shown by the broken line in FIG. In the high frequency region of several mega [Hz] to several tens of mega [Hz] due to series resonance due to the inductance of the path (about 0.1 to about 10 [μH]) and its capacitance, the leakage noise level suddenly increases near the resonance frequency. An increasing phenomenon occurs. For reference, the capacity of 4700 is shown in Fig. 3a.
"PF", inductance 1 [μH] and resistance 1 [oh
The frequency characteristic of the absolute value of the series impedance of [m] is shown. However, in the above embodiment, since the resistors 22 and 24 are connected in series to the filter capacitors 21 and 23, respectively, these resistors suppress the sharpness of the resonance as shown in FIG. It is also possible to suppress an increase in modal noise level.

Further, since the capacities of the filter capacitors 21 and 23 are as small as 2200 [pF], for example, at a commercial power frequency of 60 [Hz],
Filter capacitor 21 or filter capacitor 2
The absolute value of the impedance of 3 is about 1.2 mega [ohm]
Since it becomes sufficiently large, the series circuit of the filter capacitor 21 and the resistor 22, the filter capacitor 23 and the resistor 24
Since the commercial power source frequency component of the current flowing in the series circuit can be made to be a minute value and the power loss due to the resistor 22 or the resistor 24 can be reduced, a small resistor can be used, and it can be used for a printed wiring board or the like. Can be easily installed.

As described above, according to this embodiment, about 400 [kHz] is provided between the commercial power supply potential and the grounded casing 32.
The magnitude of the impedance decreases in proportion to the frequency up to the vicinity, and the magnitude of the impedance becomes substantially constant at a frequency of about 400 [kHz] or more, or a series circuit of the filter capacitor 21 and the resistor 22 or the filter capacitor 23 and the resistor. By connecting 24 series circuits, the effect of reducing leakage noise due to the bypass effect of the common mode noise to the housing 32 is utilized, and the excessive supply of high frequency components to the housing 32 is restricted, so that the housing 32 is protected. Suppresses the high frequency noise radiated from, and from low frequency to high frequency,
It is possible to effectively remove the common mode noise leaking to the commercial power source.

Although two resistors, that is, the resistor 22 and the resistor 24, are used in the above embodiment, the filter capacitor 21 and the filter capacitor 23 are connected in series between the commercial power sources and the connection point of both capacitors and the housing 32 are connected. One resistor may be connected between and.

The magnitude of the high frequency common mode noise changes depending on the size and shape of the housing 32, the length of the internal wiring, the positional relationship between the housing 32 and the internal electrical components and internal wiring components, and the like. However, since it is also related to the characteristics of other filter components, the capacitance values of the filter capacitors 21 and 23 and the resistance values of the resistors 22 and 24 may be selected to be optimum values accordingly. 2 of c
The frequency characteristic of the absolute value of the series impedance consisting of a capacitor having a capacity of 200 [pF], an inductance component of 1 [μH] and a resistance of 10 [ohm], and 47 in FIG.
Frequency characteristic of absolute value of series impedance consisting of capacitor with capacitance of 00 [pF], inductance component of 1 [μH] and 1 k [ohm], or frequency of absolute value of impedance shown by a and b in FIG. As shown in the characteristics, the filter capacitors 21 and 23 have a capacitance of approximately 100 [pF] to 0.01 [μF] and a resistance value of approximately 1
The maximum effect can be obtained by selecting within the range of 0 to about 10 k [ohm].

Further, when the housing 32 is made of a non-conductive material, a series circuit of a filter capacitor and a resistor may be connected between the grounded internal conductive chassis or the grounded conductive metal part and the commercial power source potential. The same effect can be obtained.

When there are a plurality of inverters, the conductive portion of the casing is grounded from the collective point of the connecting points of the two capacitors connected in series between the commercial power supply potentials of the inputs of the respective inverters. Since the same effect can be obtained by connecting via a single resistor to, the number of parts can be reduced.

The input power source may be a DC power source instead of the commercial power source 33 which is a low frequency AC power source, in which case the rectifier 26 is unnecessary.

Further, in the above embodiment, the impedance having the characteristic which is a necessary condition is obtained in the series circuit of the resistor and the capacitor. However, the impedance element having the above characteristic, for example, the high frequency loss is intentionally increased. A capacitor may be used, or a synthetic impedance synthesized by another method so as to have the above characteristics, for example,
A capacitor or the like synthesized in a distributed constant may be used.

When a resistance element such as a normal film resistor or a wire-wound resistor is used as the resistor 22 and the resistor 24, it has a minute inductance, and the capacitance of c in FIG. 3 is 2200 [pF]. Capacitor and 1 [μH]
The absolute value of the impedance may increase at high frequencies (for example, several [MHz] or more) as shown by the frequency characteristics of the absolute value of the series impedance component of the resistance component of 10 [ohm] and the inductance value of 10 [ohm]. Therefore, it has an effect of suppressing high frequency common mode noise radiated to the surroundings, and equivalently, the series resistance component may be about 10 [ohm] or more.

[0042]

As described above, according to the present invention, the direct-current or low-frequency power supply potential portion supplied to the frequency converter and the conductive portion of the case grounded to the ground by the grounding means, or the power supply potential portion and the ground. Between the conductive parts of the parts that are grounded to earth by means of the means and that are attached to or arranged in the housing, have a series resistance component of about 10 ohms or more and about 10 kilohms or less, and the absolute value of the frequency is close to the specified frequency. By connecting impedances that decrease in proportion, common mode noise in a wide frequency range from low frequencies to high frequencies can be prevented from leaking to a commercial power source by adding small components that are easy to mount in equipment. 500 [kH which cannot be sufficiently filtered by simply connecting only a filter capacitor between the DC power source potential part or the commercial power source potential part and the ground potential. It is possible to suppress the common mode noise in] or more frequencies, but can be realized with less good induction heating cooker of leakage noise.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an induction heating cooker according to a first embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram of an absolute value of impedance of a series circuit of a resistor and a capacitor according to the first embodiment of the present invention.

FIG. 3 is a frequency characteristic diagram of absolute values of series impedances of a resistance, a capacitor and an inductance component in the first embodiment of the present invention.

FIG. 4 is a circuit block diagram of a conventional induction heating cooker.

[Explanation of symbols]

 18c Ground wire (grounding means) 21 Filter capacitor 22 Resistor 23 Filter capacitor 24 Resistor 29 Heating coil 30 Inverter (frequency converter) 32 Housing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Yamashita 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A frequency converter for inputting electric power from a DC power supply or a low-frequency power supply to generate a high-frequency current in a heating coil for inductively heating a load, and a part or all of parts constituting the frequency converter. And a grounding means for grounding a conductive portion of the housing or a component attached to or arranged in the housing to the ground, and the DC power supply potential portion or low frequency input to the frequency conversion device. Between the power supply potential part and the conductive part of the case grounded to the ground by the grounding means, or the DC power supply potential part or the low-frequency power supply potential part and the grounding means grounded to the ground or attached to the case or Has a series resistance component of about 10 ohms or more and about 10 kilohms or less between the conductive parts of the parts to be placed, and the absolute value is approximately proportional to the frequency up to around a predetermined frequency. Induction heating cooker has a structure for connecting the impedance to be small.